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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 20 |
| 3 | 1680 |
| 4 | 369600 |
| 5 | 167714730 |
| 6 | 136194434423 |
| 7 | 179979692293317 |
| 8 | 361532596882040400 |
[1,1,20,1680,369600,167714730,136194434423, 179979692293317,361532596882040400] |